It is known in the field of industrial strength fabrics to make a woven scrim from thermoplastic tapes. Such tapes, commonly made of polyolefins such as high density polyethylene, stretched in the course of manufacture, are flexible, weavable and have high tensile strength. Scrims woven of such tapes have substantial mechanical strength and are used as a structural element of industrial fabrics such as tarpaulins, building covers, wrapping materials for industrial goods, and for similar uses. The strength of such scrims is limited by the number of tapes per unit area that can be woven together and the tensile strength of the individual tapes.
To produce higher strength scrims it is known to attach two or more layers together, typically by laminating or stitching. There are problems with both of these prior art methods that reduce the strength of the product. When laminating is carried out, due to the thickness of the scrims, it is difficult to cool down or temper the laminating layer, and consequently the scrim may be damaged by excessive heat, reducing its tensile strength. Alternatively, if scrim layers are stitched and sewn together, the stitches tend to create tears and splitting of the tapes and hence reduce tensile strength.
U.S. Pat. No. 6,367,513 (Cain) discloses a strengthened-scrim comprising a plain weave scrim wherein the warp and wefts ends comprise two or more superimposed tapes. However, when folded, the scrim may bend at the edges of the superimposed tapes, which, for a coated scrim, may result in cracking of the coating at the bends. Further, where more than two tapes are placed one on top of the other, difficulties arise in controlling the tension of the tapes in the middle and in adjusting the pick count according to the thickness of the ends, the number of superimposed tapes determining thickness of each end.
It is therefore desirable to provide a scrim that is woven in a multi-layer structure and wherein the aforementioned limitations are overcome, without reducing the strength of each layer and while avoiding additional processes such as laminating or sewing together of the layers, or process sophistications such as tension control in superimposing tapes.